1. Field of the Invention
The present invention relates to a heat treatment apparatus and a heat treatment method for performing the process of baking a thin film formed on a surface of a thin sheet-like precision electronic substrate, such as a semiconductor wafer and a glass substrate for a liquid crystal display device (hereinafter referred to simply as a “substrate”).
2. Description of the Background Art
Thin film formation on the substrate is an indispensable key technique for the manufacture of semiconductor devices and liquid crystal displays. For example, a resist film and an anti-reflective film are formed on a wafer in a photolithographic process for patterning on a semiconductor wafer. Also, an interlayer dielectric film for insulation and a metal film for electrode interconnection are formed on a surface of a semiconductor wafer in some cases. Further, a polycrystalline or amorphous film of silicon (Si) is formed on a glass substrate for a liquid crystal display device.
Techniques widely used for the formation of these thin films include a PVD (physical vapor deposition) process such as vacuum evaporation and sputtering, a CVD (chemical vapor deposition) process in which a film is deposited by a chemical reaction, and a coating process such as spin coating. When any of these techniques is used, there are cases where the process of baking a thin film formed on a substrate is performed. For a thin film formed by a coating process, it is necessary to evaporate a solvent in a coating solution. A thin film formed by sputtering and a CVD process is baked in some cases.
The conventional process of baking a thin film has been carried out by placing a substrate having a surface with a thin film formed thereon by the aforementioned various techniques on a hot plate and then by heating the thin film. For example, U.S. Patent Application Publication No. 2008/0008837 discloses a technique in which a coating solution for BARC (bottom anti-reflection coating) which is a type of anti-reflective film is applied to a substrate by spin coating, and the substrate is placed and heated on a hot plate, whereby the anti-reflective film is subjected to the baking process.
However, the process of baking a thin film by heating on a hot plate as disclosed in U.S. Patent Application Publication No. 2008/0008837 presents a problem such that abnormal grain growth is prone to occur in the film. Specifically, crystal grains in the film are made coarse by heating, and the abnormal growth of some of the crystal grains results in asperities on a boundary between the thin film and an underlying substrate and on a grain boundary in some cases. Under the circumstances of further developments for finer patterns in recent years, such asperities become an impediment to high-precision patterning.